Viscoelastic properties of chemically sensitive coatings can enhance the mass sensitivity of quartz-crystal-microbalance (QCM) sensors. If analyte sorption is accompanied by a change of the viscoelastic properties of the coating material, the accumulated mass cannot be calculated from the frequency shift without further information. We developed a sensor concept, which is based on a double-layer arrangement, permitting acoustic amplification and chemical sensitivity to be separated. With a proper selection of materials, the first layer realizes a constant acoustic amplification of the mass effect; the chemically sensitive layer acts purely gravimetrically. Major sensor design parameters are the shear modulus and the thickness of the first layer. From the acoustic point of view, the thickness of the chemically active layer and its material properties are less critical; a glasslike, rigid coating is preferred for a stable sensor transfer function. Simultaneous measurement of the resonant frequency of the quartz crystal and its motional resistance can be exploited to check the acoustic amplification.

Chemical Sensors based on quartz crystal resonators are often assumed to work as microbalance. In this paper we study the contribution from a viscoelastic coating to the sensor response. Different coating properties as well as analyte sorption, which may cause a pure mass increase or both a mass increase and a change in the viscoelastic parameters of the coating, are under investigation. Resonators in gaseous and liquid environments are studied.

Quartz crystal resonator measurements can be used for polymer material characterization. The non-gravimetric regime of these resonators is exploited: the electrical response of polymer-coated quartz resonators depends on the polymer shear modulus. Previously reported methods employ an electrical admittance analysis together with difficult and time-consuming data fitting procedures to calculate the film shear modulus. This contribution presents a fast and accurate three-step method for the calculation of complex shear moduli of polymer films from quartz crystal resonator measurements. In the first step, the acoustic load impedance is calculated from the electrical admittance of the quartz crystal. The key point of this method is the application of a family of approximations for the calculation of the shear modulus from the acoustic load impedance in the second step. In the third step, the best approximation is improved further in an iterative procedure.

The electrical response of chemical bulk acoustic wave sensors depends on changes in the surface mass loading and changes in the viscoelastic properties of the coating material. We consider here the acoustic behaviour and the electrical response of a quartz-crystal resonator to changes in surface mass and shear parameters of the coating material. Both a glassy and a rubbery poiymer have been investigated. The frequency changes of an oscillator are calculated from a full transmission-line model, an impedance approximation and Sauerbrey's or Martin's equation.

An application of quartz crystal resonator measurements for characterization of polymer materials is presented. It exploits the non-gravimetric response of these resonators, namely the dependence of the electrical response of polymer-coated quartz crystal resonators on the polymer's shear modulus. The possibility and an acoustic limit for this method for determination of shear moduli are discussed. It is shown that this application of quartz crystal resonators is in contrast to the well known mass detection according to gravimetric working conditions. An error analysis for the gravimetric frequency interpretation for polymer-coated crystals is presented.

The electrical response of polymer-coated quartz crystal resonators is exploited for the determination of viscoelastic properties of the polymer coating. This contribution will present a new direct method for the determination of complex shear moduli of polymer films with quart;, crystal resonators which overcomes the disadvantage of previously published time-consuming fitting procedures.

The application of quartz-crystal resonators for materials science is based on the dependence of acoustic-wave propagation on the film shear modulus and density. In contrast to the well-known chemical-sensor applications, the shear modulus determination of a thin film needs a complete electrical impedance (or admittance) analysis and a complex fitting procedure of the measured responses. This contribution concentrates on different error sources in the procedure to determine shear parameters.

Quartz crystal resonators in chemical applications are usually configured as frequency determining element of an electrical oscillator. In this paper we study the frequency shifts predicted from a full transmission line model and from common approximations of a coated resonator at the fundamental frequency as well as the 3rd and 5th harmonic. Different coating properties as well as analyte sorption which causes pure mass increase on the one hand and both a mass increase and a change in the viscoelastic parameters of the coating on the other hand are under investigation. A gaseous and liquid environment of the resonator are studied.